This invention relates to implantable osteoprosthetic devices and, more particularly, to such prostheses formed as a composite which includes a bone growth-inducing layer or coating.
Many osteoprosthetic devices, e.g., those used in the reconstruction of the hip joint, are joined to the skeletal system by impacting an anchorage component within the intramedullary canal of the bone or by mechanically fixing the device by means of a bone cement such as a polymethylmethacrylate. However, these methods are not entirely satisfactory due to the tendency of the devices to loosen upon impact or as a result of use over a long period of time.
Tissue ingrowth has also been used in attempts to anchor osteoprosthetic devices in place. In this method, the prosthesis is provided with a porous surface which is intended to foster bone ingrowth and serve as an attachment site for the new bone tissue. The tissue ingrowth approach to anchoring a prosthesis has been adopted for a variety of endoprosthetic devices.
U.S. Pat. No. 3,986,212 describes a porous polymeric coating for bone fixation by tissue ingrowth. The porous polymeric materials which are indicated to be useful are those having a specified density and interconnected pores of a specific average pore diameter. Among the polymeric materials disclosed are high density polyethylene and polypropylene or mixtures thereof having certain critical parameters. It is also indicated that the coatings can be mechanically interlocked or chemically bonded to the device.
Similarly, in U.S. Pat. No. 4,164,794, an osteoprosthetic device is coated with a porous thermoplastic material of particular properties which is said to be compatible with, and conducive for, the ingrowth of cancellous and cortical bone specules.
The anchorage component of the endoprosthetic device described in U.S. Pat. No. 4,202,055 possesses a non-porous polymeric coating in which particles of ceramic have been incorporated. Upon resorption of the ceramic particles, a polymer structure with continuous pores is formed which is penetrated by newly formed bone.
In accordance with U.S. Pat. No. 4,713,076, the anchorage component of an osteoprosthetic device possesses a completely resorbable coating which is said to enable fast and deep ingrowth of new bone tissue and anchor the implant within the bone. The coating composition is made up of a calcium compound, e.g., tricalcium phosphate or apatite (hydroxyl apatite) provided in the form of highly porous spherical particles which are embedded in a resorbable, biologically compatible binding agent such as a polyamino acid, polylactate, polyglycolate, co-condensates of these substances, gelatin or collagen.
Other types of coated osteoprosthetic devices are described in U.S. Pat. Nos. 3,808,606; 4,159,358; 4,168,326; 4,351,069; 4,365,356; 4,491,987; 4,652,459; 4,702,930; and, 4,705,694.
The use of pulverized exogenous bone growth material, e.g., derived from demineralized allogenic or xenogenic bone, is also known. See, in this regard, the disclosures of U.S. Pat. Nos. 4,485,097; 4,678,470 and 4,743,259; Bolander et al., "The Use of Demineralized Bone Matrix in the Repair of Segmental Defects", The Journal of Bone and Joint Surgery, Vol. 68-A, No. 8, pp. 1264-1273; Glowacki et al., "Demineralized Bone Implants", Symposium on Horizons in Plastic Surgery, Vol. 12, No. 2, pp. 233-241 (1985); Gepstein et al., "Bridging Large Defects in Bone by Demineralized Bone Matrix in the Form of a Powder", The Journal of Bone and Joint Surgery, Vol. 69-A, No. 7, pp. 984-991 (1987); [Mellonig], "Decalcified Freeze-Dried Bone Allograft as an Implant Material in Human Periodontal Defects", The International Journal of Periodontics and Restorative Dentistry, pp. 41-55 (June, 1984): and, Kaban et al., "Treatment of Jaw Defects with Demineralized Bone Implants", Journal of Oral and Maxillofacial Surgery, However, there is no suggestion in any of these prior disclosures of combining an osteoprosthetic component with a bone growth-inducing component based on a powdered bone material.